The present invention relates generally to high-speed reproducing systems in apparatuses for reproducing information signals recorded on rotary recording mediums, and more particularly to a system for reproducing, at high-speed, recorded information for the purpose of searching for the position of a specifically desired information content from among information contents recorded on the rotary recording medium.
Known system for recording and reproducing information signals (such as video signals and/or audio signals) on and from disc-shaped, rotary mediums (referred to hereinafter simply as "discs") are broadly divided into system using optical reproduction, systems using a reproducing stylus employing a piezoelectric element, and systems utilizing variations in the electrostatic capacitance between an electrode on the reproducing stylus and the recorded surface of the disc.
In accordance with a known electrostatic capacitance system, recording is accomplished by forming a spiral guide groove in the disc for guiding the reproducing stylus. As the same time, pits are formed in responsive correspondence with an information signal as it is recorded on the bottom surface of the groove. In the reproducing system, the reproducing stylus is guided by the guide groove. The stylus traces the track within the groove and reproduces the signal in response to variations in the electrostatic capacitance.
In this known system, however, a reproducing stylus guiding groove is provided on the disc. The reproducing stylus is compulsorily guided by this guide groove. It is not possible for such a reproducing stylus to undergo relocation operations such as riding over the groove wall of one track, moving into another track and returning to the original track. If the reproducing stylus were to be forced to undergo such an operation, the groove and the stylus would be damaged. For this reason, it has not been possible in this known, groove type, system to carry out special reproduction such as quick-motion picture reproduction, slow-motion picture reproduction, still-picture reproduction, and random access motion.
Accordingly, with the aim of overcoming the various problems of the known systems described above, a novel "Information signal recording and reproducing system" is disclosed in the specification of U.S. patent application Ser. No. 785,095, filed Apr. 6, 1977. According to this system, the recording system forms pits in accordance with the information signal being recorded along a spiral track on a flat disk shaped recording medium, without forming a groove therein. In the reproducing system, a reproducing stylus traces over and along this track, thereby reproducing the recorded information signal in response to variations in the electrostatic capacitance.
In this system, there is no groove for guiding the reproducing stylus on the disc; therefore, pilot or reference signals should be recorded on or in the vicinity of a track of information signal, such as a video signal, on a rotary disc. At the time of reproducing, the reference signals are reproduced together with the video signal. Tracking servo control is carried out so that the reproducing stylus traces accurately along the track in response to the reproduced reference signals.
By the use of this previously described system, the recording track has no groove. There is no possibility whatsoever of the reproducing stylus or the recording medium being damaged by crosstrack stylus movement. The stylus can trace the same portion of the track repeatedly many times, with a so-called random access motion, wherein a reproducing stylus is moved at high-speed to a desired position on a disc to reproduce a desired information. In addition, a special reproduction such as still, slow motion, or quick motion reproduction becomes possible.
Already known are systems for quickly shifting the reproducing stylus to the position of a specifically desired information signal recorded on a disc and commencing reproduction from that position. One of these systems is the random access system in which address signals are used. Another system is the so-called "live search" system wherein, as the reproduced picture is observed, the reproducing stylus is shifted at high-speed until the desired image is obtained.
Of these systems, the random access system makes use of address signals respectively recorded on all track turns of the disc, and the reproducing stylus is shifted as it reproduces these address signals. Then, when the reproduced address signal coincides with the address of the desired designation, the movement of the reproducing stylus is stopped.
One example of this random access system is described in detail in the specification of U.S. patent application Ser. No. 962,795, filed Nov. 21, 1978, entitled "Random access system in a rotary recording medium reproducing apparatus", now abandoned and replaced by U.S. patent application Ser. No. 156,118, filed June 3, 1980.
However, while this random access system has an advantage in that the reproducing stylus can be shifted accurately, positively, and quickly to any desired position, it has a drawback in that its reproducing apparatus tends to become relatively complicated and expensive.
In contrast, the above mentioned live search system does not employ address signals and does not require components such as circuits for reference to and attaining coincidence with address signals, whereby its reproducing apparatus is advantageously inexpensive.
However, since merely shifting the reproducing stylus at high-speed in the radial direction of the disc will not bring the stylus onto a track in tracing state, a reproduced image cannot be obtained. Accordingly, in this live search system, it is also necessary to keep a tracking servo system as mentioned hereinbefore in an operating state to exercise control so that the reproducing stylus will trace along the track in the reproducing system. However, if the reproducing stylus is shifted at high-speed with the tracking servo system in its operating state, the reproducing stylus will undergo the following operation.
As the reproducing transducer including the reproducing stylus is fed at high-speed, the stylus undergoes tracking control up to the elastic deformation limit of parts such as the cantilever holding the stylus and the damper and maintains its state of tracing along one track turn. Thereafter, when the deformation of the above mentioned cantilever, damper, etc., exceeds the above mentioned limit, these parts are restored to their original natural state. For this reason, as a result of their elastic restoring force, the stylus skips over a number of hundreds, for example, of track turns and again traces by being tracking controlled along a new track turn. Thereafter, the above described operation is repeated.
As a consequence, the reproduced picture is formed by randomly reproduced information signals, at intervals of a number of hundreds of track turns. For this reason, the information content is missing at every interval of a few hundred track turns. Consequently, the movements of the reproduced image become intermittent, whereby it is impossible to determine accurately and positively the recorded position of the specifically desired information content. Another problem which arises is that, since the parts such as the cantilever and damper undergo repeated deformation up to the above mentioned limit and restoration, they are subjected to damage.
Another practice known in the art is to obtain a quick-motion reproduced image by forcibly shifting the reproducing stylus while it is tracing each track turn on the disc to the adjacent track turn during the vertical blanking period of every field of the video signal. By this system, however, in the case where a video signal for four fields, for example, is recorded along the track, and the stylus is shifted once during every vertical blanking period, a forward quick-motion reproduction of a maximum of quintupled speed is the limit, and the speed cannot be raised any higher. However, in order to search for and determine a specifically desired position on disc in a short time, it is necessary that a reproduced image varying with a speed which is 10 to 200 times that at the time of ordinary reproduction be obtainable as the reproduced image. For this reason, by this quick-motion system, the reproducing stylus cannot be shifted to a desired position in a very short time.
Accordingly, there has been a method wherein, by further expanding the above mentioned quick-motion operation, the reproducing stylus is shifted by a plurality of track turns within the above mentioned vertical blanking period. However, since a time of 0.2 to 0.3 milliseconds is required for the reproducing stylus to shift to the adjacent track turn, the vertical blanking period is exceeded in some cases by the period for the stylus to shift over a plurality of track turns. In such cases, a disturbance occurs in the reproduced image, and the picture quality deteriorates. Furthermore, even with this shifting of the stylus over a plurality of track turns every field of the video signal, searching for and determining a desired position cannot yet be accomplished with amply high-speed.